The Spanish opening, one of the oldest known chess openings, is still highly popular at every level of the game. It leads to highly complex play, whichever variation arises. In this volume of the "Mastering" series, the authors explain, with the aid of many diagrams, the essential features of the main variations of the Spanish opening. This series organizes the subject matter according to strategic themes and, by concentrating on the essentials, the books ensure that the reader genuinely understands the underlying principles instead of merely memorizing variations.